Serial communication is common in industrial control applications. For example, serial half-duplex communication in accordance with RS-485 is widely used in automation systems. Applications such as factory automation systems often employ programmable logic controllers that use RS-485 for communication. Some systems are moving to Ethernet based communication, but still require support for prevalent legacy systems. RS-485, for example, does not specify speed, format and protocol of the serial communication. Interoperability of even similar devices from different manufacturers is not assured by merely complying with the signal level specifications.
An example of a prior art communication system using serial half-duplex communication is illustrated diagrammatically in FIG. 1, wherein an integrated circuit 10 (e.g., a RISC microprocessor), including a host processor 11 and a universal asynchronous receiver/transmitter (UART) 12, cooperates with an external transceiver (XCVR) 13, for example, a further integrated circuit. The UART 12 outputs to the transceiver 13 data TXD, which has been received from the host processor 11 and is transmitted by the transceiver onto a devices bus that has one or more connected devices, as illustrated diagrammatically at 14. Similarly, the UART 12 receives from the transceiver 13 data RXD, which has been received by the transceiver 13 from the devices bus 14. The UART 12 provides this received data to the host processor 11. The host processor 11 provides to the transceiver 13 control signaling TX/RX that appropriately enables and disables transmit operation and receive operation of the transceiver 13.
A turn-around operation occurs when the host processor 11 (using the TX/RX signal) switches the transceiver 13 from a transmit (TX) mode to a receive (RX) mode, or vice versa. Turn-around time for transition from TX mode to RX mode, for example, is the time required to transition the transceiver 13 from the TX mode, where transmit and receive operations of the transceiver 13 are respectively enabled and disabled, to the RX mode, where transmit and receive operations of the transceiver 13 are respectively disabled and enabled. This turn-around time begins when the last transmitted bit has completely traversed the transceiver 13.
For communication in many automation system applications, low latency, even aggressively low latency, is important. This means, for example, that the turn-around from TX mode to RX mode should happen as soon as possible after the last transmitted bit has traversed the external transceiver (e.g., 13 in FIG. 1). That is, the turn-around time from TX mode to RX mode should be as short as possible.
It is desirable in view of the foregoing to provide for reducing turn-around times between the TX and RX modes of a serial half-duplex transceiver coupled externally to an integrated circuit.